1. Field of the Invention
The invention concerns respiratory masks, especially of the type useful for protecting the wearer against gases and vapors.
2. Description of the Related Art
Respiratory masks which feel the most comfortable to wear have a facepiece molded of a soft, compliant rubber formed with an inturned cuff or flap having a feathered edge that forms a hermetic seal against the wearer's facial skin. Because of the softness of the rubber, major surfaces of typical facepieces are rather thick to provide enough body to bear the weight of the cartridges while also supporting an exhalation valve. See, for example, FIG. 4 of U.S. Pat. No. 2,652,828 (Matheson). The thickness of the rubber can make the mask heavy to wear. In order to achieve adequate service life in protecting against gases and vapors, respiratory masks typically utilize two rather large and heavy filters which can add greatly to the weight felt by the wearer.
When a respiratory mask has a fitting in each cheek area for a filter cartridge, the fittings and cartridges typically are formed with mating threads to permit the filter medium to be replaced. See, for example, FIG. 10 of U.S. Pat. No. 4,414,973 (Matheson et al.). When replaceable filter cartridges are screwed into place, they can leak if cross-threaded or if not screwed in tightly at all times during use. Screw-in cartridges typically are round to facilitate threading. If a holder for a screw-in cartridge were asymmetric, it could be accidentally rotated into the wearer's field of vision when the cartridge is tightened.
When harness attachments are fastened to the facepiece as in FIG. 1 of the Matheson et al patent, the facepiece must be thick enough in the attachment areas to withstand forces applied in strapping the facepiece to the wearer's head, thus adding additional weight.
Respiratory masks which have a single filter cartridge involve the same problems. See, for example, U.S. Pat. No. 4,155,358 (McAllister et al.) which shows a valveless respirator having a single oval-shaped chemical cartridge.
Filter media which do not protect wearers against vapors and gases typically are of substantially lower weight than those which do. Such a respiratory mask is shown in U.S. Pat. No. 4,592,350 (Maryyanek et al.) wherein "Two inhalation valve mechanisms 24 are positioned through circular holes in the facepiece body in opposing positions on either side of the wearer's mouth" (col. 3, lines 59-61). "Triangular-shaped filter covers 16 snap onto each of the filter holders 22 to contain and protect the filter 14" (col. 4, lines 54-55). The filter covers are asymmetrically mounted to extend laterally from the cheek areas, so that the filter media can have larger areas than would be feasible for a circular filter cartridge. Even though particulate filter media can be of much lighter weight than filter media which are effective against gas vapors, FIG. 2 of Maryyanek patent shows that its facepiece 12 is much thicker where it supports the filter holders than it is at the feathered cuff or flap. Hence, the Maryyanek mask may be rather heavy to wear even with lightweight filter media.
The Maryyanek patent does not suggest that the filter holders are held in place by anything but friction, probably to permit the filter holders to be removable for cleaning. Hence, if Maryyanek's filters were exchanged for gas and vapor filters, their greater weight could cause accidental rotation of the filter holders.
When a respirator mask has a single filter cartridge, the cartridge can be swept back along both cheeks of the wearer as illustrated in FIG. 9 of U.S. Pat. No. 4,501,272 (Shigematsu et al.) which concerns a particulate respirator mask. Such a respirator mask can have either one or two inhalation valves. Another such respirator mask having a single swept-back filter cartridge is shown in U.S. Patent No. 4,630,604 (Montesi) which also concerns a particulate respirator mask. Its inhalation and exhalation valves are coaxial.
Scott (a Figgie International Company in Lancaster, N.Y.) markets a Model 66 respirator mask with a half facepiece consisting of a rigid member fitted into a soft, compliant "face seal". The rigid member has a central aperture for an exhalation valve and a pair of swept-back cheek portions. A cylindrical projection from each cheek portion is externally threaded to receive a cylindrical filter cartridge.
Scott also markets a Model 65 respirator mask which has a full facepiece consisting of a transparent rigid member fitted into a soft, compliant face seal. Its rigid member has only one opening for an assembly containing an exhalation valve and two filter cartridges.
U.S. Pat. No. 4,549,543 (Moon) shows a respiratory mask that apparently is intended only to protect against particulate matter. It has a single filter cartridge which is located under the user's chin for aesthetic purposes. Also for aesthetic purposes, the facepiece is formed of flexible transparent sheet material such as polyethylene or polyvinyl chloride.
For other respirator masks, see U.S. Pat. Nos. 2,662,887 (Green) and 2,505,173 (Conley).
2. Other Prior Art
While the following patent does not concern respiratory masks, it is of interest in having a similarity to the respiratory mask of the present invention.
U.S. Pat. No. 3,330,274 (Bennett) shows a face mask fitted with a flexible conduit to suitable respiration apparatus, primarily for the medical treatment of respiratory disorders. As seen in FIGS. 1 and 2, the face mask consists of a "face piece 12" of relatively stiff and transparent plastic material and a "resilient, deformable sealing cuff 14" extending entirely around the perimeter of the face piece.